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Full text of "Handbook Of Chemical Engineering - I"

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458
CHEMICAL ENGINEERING
Thwing instrument is so constructed that the source must have a diameter at least one-eighth of the distance from the source to the receiving tube. Thus at 8 ft. from a furnace the opening into the furnace must be 1 ft. in diameter. For permanent installations the tube is ventilated and has several extra diaphragms to prevent local heating of the instrument and reradiation to the couple.
Figure 22 illustrates the principle of the Foster radiation pyrometer made by the Taylor Instrument Cos.   The thermocouple 6 and a front diaphragm B are located
FIG. 22.—Foster radiation pyrometer.
at the conjugate foci of a concave mirror DD'. As in the case of the Thwing pyrometer, the source must be large enough to fill the cone of rays denned by the angle a or the lines A'CA". The position of the point C is marked by a wing nut on the telescope tube. The angle a. is made such that the diameter of the source sighted upon must be at least one-tenth the distance from the source to the wing nut. Thus for a
FIG. 23.—Fery radiation pyrometer.
distance of 10 ft. the diameter of the opening into the furnace must be at least 1 ft The Brown Instrument Co. makes a radiation pyrometer which is similar in principle to the Foster pyrometer. The receiving tube of the Brown radiation pyrometer is made collapsible for convenience in carrying.
Figure 23 is a cross-section drawing of the Fery pyrometer made by the Taylor Instrument Cos. Radiation from the source sighted upon is concentrated by the concave mirror of speculum metal or sold, upon the hot iunction of a minute ttiMrvm-